The present invention relates to a back lighting device for a liquid crystal panel, for irradiating a transmissive panel from the rear.
Recently, thin display devices provided with back lighting mechanisms have been used as the display devices for word processors, lap-top computers, and the like. The back lighting makes it easy to see the information on the screen.
Examples of such back lighting mechanisms include one in which a plurality of luminous bodies such as cold cathode tubes or the like and a light scattering plate are disposed just under a panel, one constituted by an electroluminescence (EL) face luminous body, and so on. In those back lighting devices, however, there have been problems, such as the display device being relatively thick, in the case of the former example, or the display device having insufficient luminance and a relatively short life, in the case of the latter example.
There have been various trials on back lighting devices of the type including a photo-conductive plate having a linear light source on a side edge portion of a transmissive plate. However, light entering through the end surface of the transmissive plate cannot be luminous in a face shape without any change, so that it is necessary to make the light emitting surface and/or the back surface of the transmissive plate subject to a treatment such as surface roughing, application of a light scattering material thereon, or the like. If such treatment is performed uniformly over the entire surface of the transmissive plate, however, the farther from the light source, the lower the luminance. It is accordingly necessary to change the treatment condition in order to make the luminance uniform. To this end, various devices have been made.
Further, there have been proposals in which a groove is formed in a transmissive plate per se, and others in which a transmissive plate is formed in a wedge shape. Nevertheless, it has not yet been possible to provide uniform light distribution.